A method of forming a color image by developing exposed silver halide grains with an aromatic primary amine developing agent of followed by coupling the oxidation product of the developing agent formed by the development and a color coupler, is a technique which has heretofore been well known. Such a method is widely utilized as a so-called silver salt photographic method.
One constant important consideration in the photographic field is to effect development of photographic materials as rapid as possible in view of the necessity of improving the producibility in the laboratory and of shortening the customers' waiting time.
The easiest way of accelerating development of photographic materials is to elevate the processing temperature so as to activate the processing reaction. In such a way, noticeable shortening of the time required for the step of development has already been achieved.
Many patent publications illustrate rapid development of silver halide grains having a high silver chloride content (for example, JP-A-58-95345 (corresponding to U.S. Pat. No. 4,565,774), JP-A-59-232342, JP-A-60-19140; the term "JP-A" as used herein means an "unexamined published Japanese patent application"). In accordance with such illustrated techniques, the time for color development, which was generally 3 minutes or more, could be shortened to one minute or less by the use of such high silver chloride content silver halide grains. However, it has been found that when the processing time is further shortened to 20 seconds or less, the photographic properties are generally unstable and, in particular, the tone-reproducibility of the processed materials is unstable.
Other means of effecting high-speed development include a technique of using a color development accelerator (for example, JP-A-53-15831, JP-A-55-62450, JP-A-55-62451, JP-A-55-62452, JP-A-55-52453, JP-B-51-12422, JP-B-55-49728; the term "JP-B" as used herein means an "examined Japanese patent publication") and a technique of using a so-called auxiliary developing agent such as 3-pyrazolidones (for example, JP-A-60-26338, JP-A-60-158444, JP-A-60-158446). However, photographic materials processed by the use of such additives are known to have a drawback in that the storage stability of the processed materials is insufficient.
On the other hand, to achieve the desired effect some patent publications define the ratio of the mean grain size between plural types of silver halide grains constituting photographic materials (for example, JP-A-61-38944, JP-A-62-6247, JP-A-62-3248, JP-A-62-40456, JP-A-62-62358, JP-A-62-172348 (corresponding to U.S. Pat. No. 4,745,047), JP-A-62-253148, JP-A-63-71839 (corresponding to U.S. Pat. No. 4,803,152), JP-A-63-71838, European Patents 0248442-A2, 0230997-A2, U.S. Pat. No. 4,745,047). However, all of the photographic materials illustrated in these publications could display the effect only when they are processed for a relatively long period of time. The present inventors found, however, that the silver halide grains in the photographic materials illustrated above could be sufficiently developed for such a long period of time, but suffered from an almost complete dissolution of the grains. Therefore, one characteristic aspect of the present invention is to prevent the over-dissolution of the grains, and/or to control the dissolution in a desired range so as to impart favorable properties to the processed photographic materials.
As opposed to the above-illustrated previous techniques, high-speed development, the goal of the present invention (i.e., to complete development of photographic materials in an extremely short period of time), causes a problem in that so-called tone-reproducibility varies and good images could not be stably formed. The point to be noted in this respect is that the developability of silver halide grains in the extreme initial stage of development is poor.
In a high-speed development similar in objectives to the present invention described hereinafter, the developing agent and alkali agent, which are the main components in the developer, could barely reach the deepest portions of the photographic light-sensitive layers of the material to elevate the pH value of the material to at least the required level. To do so, the developer components had to overcome the acid components present in the deep portions of the photographic light-sensitive layers. Thus, it is necessary that the exposed photographic material is developed without delay. Accordingly, it is necessary that use of such a substance that would adsorb to silver halide grains, thus retarding the development reaction, is avoided as much as possible in such high-speed development. From this viewpoint, the known method of controlling the amount of the development-inhibiting compound so as to ensure the stability of the photographic properties of photographic materials to be processed, is not suitable to high-speed development to be effected in a short period of time, since the presence of such compounds would retard the development as a whole.
On the other hand, another desired feature of high-speed development to be effected in a short period of time is that the development when initiated as mentioned above should be completed as quickly as possible. In general, the individual silver halide grains in a photographic emulsion each have a slightly different sensitivity even though the grains as a whole may have an extremely narrow grain size distribution. Additionally, the exposure amount is not always the same in all the individual grains. Therefore, the development-initiating time and the development-finishing time during the development procedure would generally vary amongst the individual silver halide grains. Accordingly, it is necessary to eliminate the factors which would cause retardation of initiation of development of silver halide grains or would cause retardation of the completion of development thereof, as much as possible, in order that the development is effected to a practically necessary degree within a predetermined development time. From this viewpoint, the method of elevating the ratio of silver bromide to silver chloride in a portion of or in all of the silver halide grains in the photographic emulsion layer thereby to control the development speed of the silver halide grains to ensure the stability of the photographic properties, is not adequate, since development could not be finished within a pre-determined period of time. Therefore, a method of stably forming a color image without retarding development is. strongly desired which avoids the drawbacks mentioned above.